Synergistic effect of entomopathogenic nematodes and thiamethoxam in controlling Bradysia odoriphaga Yang and Zhang (Diptera: Sciaridae)

Abstract

Six entomopathogenic nematode species (EPNs) (Heterorhabditis bacteriophora H06 (H06), Steinernema carpocapsae NC116 (NC116), Steinernema carpocapsae All (All), Steinernema longicaudum X-7 (X-7), Steinernema feltiae SF-SN (Sf) and Heterorhabditis indica LN2 (LN2) were tested for virulence against 3rd instar Bradysia odoriphaga, and their interactions with thiamethoxam against 3rd instar B. odoriphaga under laboratory and greenhouse conditions were also evaluated. S. feltiae SF-SN, which is the most virulent, was selected to evaluate the synergism effects with thiamethoxam at different concentrations under laboratory conditions. S. feltiae SF-SN and thiamethoxam were either applied alone or in combination, and the combined application manner was evaluated in the greenhouse. Under laboratory conditions, a synergistic effect was found between six EPNs and thiamethoxam. The combination effects of Sf, All and LN2 species caused significantly higher mortality than the other three treatments (X-7, H06 and NC116). Furthermore, the combination of Sf and All species led to a significantly higher control effect than LN2 in greenhouse tests. In further greenhouse tests, the combination effect of Sf (0.75 billion IJs/ha)+thiamethoxam (1.0kg a.i./ha) applied twice (28day intervals) was significantly higher than a single treatment of Sf+thiamethoxam at twice the dosage. Compared to the single thiamethoxam application, the combination effects of Sf and thiamethoxam had the highest value at over 90% of the control effects for up to 6weeks. Therefore, the integrated technique of the synergism of S. feltiae SF-SN species and thiamethoxam to control B. odoriphaga could be useful for integrated pest management in the future.